OFDM technique is publicly recognized as a key technique in the new generation wireless communication system. It can effectively resist inter-symbol interference (ISI) and multi-path fading resulted from multi-path, converting a frequency-selective fading channel into several frequency-nonselective fading channels. However, the OFDM technique is highly sensitive to transceiving carrier frequency offset, which will lead to the ICI, and thus affect the performance of the whole system.
The paper “OFDM for wireless multimedia communications” (Norwood, M A: Artech House, 2000) authored by R. Van Nee and R. Parasad discloses a method for shaping pulse for each transmitting subcarrier at the transmitting end, which is equivalent to performing windowing for the output of Inverse Fast Fourier Transform (IFFT). However, this method can only reduce the out-of-band emission of the OFDM communication system, but not the ICI. This is because in the practical OFDM system, each OFDM symbol has cyclic prefix to resist ISI, the window function only influences the cyclic extension part of the signal, but the original part of the signal does not change; while at the receiving end, only the original part of the signal is performed Fast Fourier Transform (FFT).
The paper “Reduced ICI in OFDM systems using the “Better than” Raised-Cosine pulse” (IEEE Commun. Lett. Vol. 8, No. 3, pp. 135-137, March 2004) authored by P. Tan and N. C. Beaulieu discloses a method for reducing ICI by the means of windowing at the transmitting end, which, however, is only applicable to the classical OFDM symbol which has no cyclic prefix.
The paper “Improving an OFDM reception using an adaptive Nyquitst windowing” (IEEE Trans. Consumer Electronics, Vol. 42, No. 3, pp. 259-269, August 1996) authored by C. Muschallik discloses a technique of windowing before performing FFT at the receiving end, wherein, the function range of the window function is the original signal part and the part not interfered in the cyclic prefix; the window function must satisfy Nyquist criterion so that there will be no ICI when there is no carrier frequency offset; and the roll-off coefficient of the window function is adaptive to the change of channel, if the part not interfered in the protecting interval is large, then relatively great roll-off coefficient can be used to better reduce the ICI. The main disadvantages of the method are: (i) since the unconsumed protecting interval is generally very small, the chosen roll-off coefficient will also be very small, and thus the ability of suppressing ICI is very limited; (ii) only the raised cosine function is chosen as the window function, which is not the optimal choice.